Powered electric Wheelchairs come with a relatively few
"standardised" battery case sizes. When talking about powerchair
batteries "Group 27","Group 24", Group 34" and "Group 22NF" size batteries are
often specified for each different model. These are the four sizes most
manufacturers use. Deep Cycle mobility
batteries are available from many companies in these four sizes.

At the bottom of this page is a table
specifying the actual dimensions of these BCI Standard battery sizes.

We don't really need to know the actual
sizes unless you are trying to fit a different battery size than your
manufacturer specifies. Which is often possible!

My own powerchairs for e.g. originally used a group 34 battery
of 56ah. (Amp Hour capacity) As specified by the manufacturer, Sunrise medical.

But knowing the actual dimensions of a group 34 battery
allowed me to know a larger capacity group 24 battery would also fit.

How? Well that's easy! A
group 34 is the same length, and the same width as a group 24 battery. Bit the
group 24 battery is taller.

So I just looked at the space above the batteries and decided
that the taller group 24 ones would also fit.

Group 27 batteries
are around the 90 to 105Ah capacity but much longer. And heavier. Making
powerchairs too big for sensible indoor usage and very heavy. "Bounder
Wheelchairs" use these in some powerchairs. And many off road all terrain and
4x4 outdoor powerchairs use them too.

Group 22 batteries
are considerably smaller capacity (see table) and smaller sized physically too. In general group 22
batteries are good only for slow 4mph mostly indoor powerchairs and are limited
in range. If you are serious about powerchairs absolutely avoid powerchairs that
use these!

Group 34 batteries
are typically 50Ah to 70Ah and are (or can be) almost as good for range as the taller
group 24 batteries. And in certain cases better for heavy loads. A standard
automotive starter battery size case with mounting lips at the bottom. Depending on actual battery chosen***. These are
generally good in all indoor / outdoor powerchairs up to 6 mph and often used
where seat electronic riser mechanisms take the space that that the similarly
sized footprint but taller Group 24 batteries needed. Some like the Odyssey
batteries are exceptionally good.

Group 24 batteries
are taller deep cycle case versions of the group 34 ones above. They are usually 70 to
75Ah and
for most indoor / outdoor 6mph powerchairs are the only sensible option if Gel
batteries are used.

*** I PERSONALLY use Group 34 Hawker
Odyssey 68Ah AGM batteries in my home built powerchair (even though I
designed it to take group 24 batteries) since they can make much more current
(power) when used in extreme conditions off road/beach/snow etc than any group
24 Gel battery. And the capacity is almost as high too.

And they also have equally as good a range as the bigger
(taller) group 24
batteries due to a lower internal resistance value than Gel batteries that is
typically half or even better... So if you are currently using and limited to group 34 batteries
take a look at the Odyssey PC1500DT battery! It can be charged in 1 hour
too...

And if space is tight remember that these are the MAXIMUM permissible sizes
for each "class" of battery in the chart below. So actual measurements cannot exceed this chart
usually...
But some batteries are notably smaller in one dimension or another. EG the Group
34 Optima Deep Cycle battery is shorter than the allowable 260mm, And the
Odyssey is bigger (longer).

CAUTION - Having said all that, this Odyssey
battery below is a D34 (Group 34) battery. But is about
14 mm (half inch) wider at the top than the table above says it should be!

Battery sizes are at best "nominal" values it seems... So it still pays to
measure them. This is because D34 batteries are an automotive size. They
are the correct size at the bottom where it would fit into the battery tray in
your car. But the top is less important. They also have a lip at the bottom for
an automotive battery bolt on style clamp.

So in the case of D34 batteries especially it pays to read the specs specs for the actual
battery you wish to buy. Most powerchairs will have room at the top for an extra
7mm length each side (14mm extra width) but some may not! So it pays to measure exactly.

This one below is actually the battery I prefer over all of the group 24 Gel batteries
that most top end powerchairs come with. It handles big currents that I need
without "sagging" and fast
charging is much better/faster. Although it has a slightly lower deep cycle life
expectancy.